Fixing decaying infrastructure involves disposing and replacing the existing structures, processes which generate heat and carbon dioxide (CO2). There are economic and environmental advantages to repair rather than replace cracked structures. However, repair is a slow, exothermic process involving agents such as epoxies and microbes, and results in structures with reduced strength and reliability.
Concrete in its many forms is the single most used construction material in the world, and while a comparatively low producer of carbon emissions by itself, the sheer volume constitutes a significant fraction of man-made global carbon emissions (about 1514 million metric tons of CO2 in 2009).1 A cumulative degradation caused by salts, alkalis, freeze-thaw cycles, carbonation, and physical wear is inevitable. Known repair processes for cracked and damaged concrete typically rely on matching dissimilar materials, such as inorganic calcium-silica-hydrate (C—S—H) compositions with organic petroleum-derived epoxies. Patching and resurfacing success generally relies on artisanal skill, but can, in itself, cause further damage, potentially undermining the process.2 
One alternative is biocalcification by use of carbonic anhydrase (CA)-producing microbes to fill gaps, cracks and fissures in concrete. CA is a natural enzyme that is found in all living organisms, including humans. The CA enzyme catalyzes the reaction between calcium chloride (CaCl2) and carbon dioxide (CO2) to produce calcium carbonate (CaCO3). Calcium carbonate self-assembles on smooth and fractured cement paste surfaces to produce stable crystal structures that fills cracks with solid precipitate. The CA enzyme can be employed to produce calcium carbonate at a rapid rate. Also, in contrast to other repair materials, such as organic epoxies, calcium carbonate is a material with similar mechanical properties to cement paste and will produce a final product that is indistinguishable from the original fault-free product. This will also substantially avoid stress concentration arising from dissimilarities among repair and substrate compounds. Importantly, CA enzyme-catalyzed calcium carbonate consumes atmospheric carbon dioxide and decomposes without odor or any risk to human health.
However, use of bacteria or microbes to precipitate calcium carbonate typically mandates subsequent sterilization, such as by applying high-pressure steam, or potentially toxic chemicals. Biological non-enzymatic approaches employing microorganisms such as bacterial spores are currently practiced, but such methods typically lack the speed and specificity of the CA enzyme, and a much greater amount of biomaterial must be consumed.
Even so, the use of bacteria and attendant antibiotics to repair concrete structures, such as buildings that are in direct contact with humans, poses health risks. Existence of spores also creates unpleasant odor when not dormant that will always coexist with the structure. Generally, known methods of concrete repair by use of microbial CA creates environmental and occupational hazards. Moreover, calcite growth by use of bacteria or microbes is also quite slow, and repair of large cracks and pores is not pragmatic as it requires an extended period of time. In addition, the process is limited to a certain class of structures because the bacteria typically retreat to a spore stage and persist. These factors essentially make the use of spores as a self-healing agent only viable for a very limited class of structures.
Therefore, there is a need for a method of repairing cracks and fissures in cementitious surfaces that overcomes or minimizes the above-referenced problems.